The present invention relates to an apparatus and a method for indirectly estimating and detecting a temperature of an exhaust gas purification catalyst mounted to an exhaust system in an internal combustion engine.
In order to detect a catalyst temperature representing an active state of an exhaust gas purification catalyst, a temperature sensor is provided to a catalyst to detect the catalyst temperature or a heat supply amount from the exhaust gas to the catalyst is calculated to detect the catalyst temperature. The former is disclosed in Japanese Unexamined Patent Publication 5-200249, and the latter in Japanese Unexamined Patent Publication 9-108543.
However, the provision of the temperature sensor brings cost-up, while the estimation of temperature is difficult to ensure a sufficient accuracy.
The present invention, in view of the above conventional problems, has been achieved and an object of the invention is to detect a temperature of an exhaust gas purification catalyst in an internal combustion engine with high accuracy.
Another object of the present invention is to detect a temperature of an exhaust gas purification catalyst by the estimation computation without a need of providing a temperature sensor and a cost-up due to the provision of temperature sensor.
A further object of the present invention is to improve an exhaust gas purification performance by accelerating an air-fuel ratio feedback starting time as early as possible due to high accurate estimation and detection of a catalyst temperature.
The present invention is constituted as follows in order to achieve the above objects.
An impedance of a sensor element of an air-fuel ratio sensor mounted to an exhaust system in an internal combustion engine is detected.
Then, a temperature of an exhaust gas purification catalyst mounted to the exhaust system as well as the air-fuel ratio sensor is detected by estimating computation based on the detection value of the impedance.
Namely, since a heat capacity of the sensor element is small, a temperature of the sensor element is substantially the same as a temperature of the exhaust gas passing through the air-fuel ratio sensor. On the other hand, the impedance of the sensor element is decreased with the increase of the temperature of the sensor element. Accordingly, the temperature of the sensor element and further the temperature of the exhaust gas flowing in the air-fuel ratio sensor can be estimated by detecting the impedance.
The temperature of the exhaust gas purification catalyst is substantially equal to the temperature of the exhaust gas flowing in this catalyst, which is close to the temperature of the exhaust gas flowing in the air-fuel ratio sensor. Therefore, as a result, the catalyst temperature can be estimated accurately based on the detection result of the impedance of the air-fuel ratio sensor.
In an apparatus where air-fuel ratio sensors are disposed upstream and downstream of the exhaust gas purification catalyst, by using both impedances of the sensor elements of these air-fuel ratio sensors or placing more importance on the impedance detection value of the sensor element more closely related to the catalyst temperature estimation, the temperature of the exhaust gas purification catalyst can be estimated more accurately.
The other objects and features of this invention will become understood from the following description with accompanying drawings.